Not Applicable
Not Applicable
The invention relates in general to conduction cooling of surfaces and in particular to conduction cooling of heat generating components, such as high power semiconductors and integrated circuits (IC""s), where variations in gap distance and/or angular misalignment (tilt) between its surface and a cooling surface must also be accommodated. The invention may produce embodiments to interface between surfaces with various shapes, including, but not limited to: flat, two-dimensionally curved, three-dimensionally curved, cylindrical and tubular surfaces. The invention also relates to simple methods of making the devices.
Continuing demands in electronic technology of greater integration, faster operating speeds, greater output power, and reduced package size have increased the density of heat generation and magnified cooling requirements. Further, electronic components are often sealed in modules to protect them from liquid cooling systems or harsh environments. Manufacturing tolerances and thermal expansion properties of the various items along the thermal path, however, can combine to create conflicting thermal effects. Ignoring these effects can result in large mechanical stresses, inconsistent thermal contact, erratic functioning of the component, and premature component failure. A compliant, thermally conductive interface device is often needed between a heat generating component and a module cover plate or heat sink to accommodate manufacturing tolerances and thermal effects, reduce mechanical stresses, and provide consistent cooling performance. In addition, similar interface devices are often needed with components having curved or cylindrical surfaces, such as traveling wave tubes and heat pipes. Many designs have been developed to address these needs. A few of the more relevant designs are briefly described below.
U.S. Pat. No. 4,485,429, describes a plurality of thin wires anchored to a cover plate that press down onto a heat generating component causing the individual wires to bow in a springlike action to accommodate component height and tilt. Although each thin wire has high thermal resistance, filling the space above the component with a plurality of wires reduces the overall thermal resistance to a low level. Bowing of the wires, however, must be limited (approximately 0.13 mm compression) to retain elastic springback capability and prevent excessive spreading of the wire bundle in a fan-like (or broom-like) manner. Excessive fan-like spreading can reduce thermal contact efficiency between the ends of the wires and the component surface, and reduce wire density over the component. U.S. Pat. No. 4,156,458 describes a similar system using foils instead of wires. Straight foils are stacked against each other (without gaps) and bonded to a cover plate at an acute angle (45). Soldering the foils to a component surface (after fan-like spreading of the foil bundle) is also described to complement thermal contact. Soldering, however, stiffens the foils, increases resistance to further compression, and can impose lateral forces on the component due to the angular alignment of the foil bundle.
U.S. Pat. No. 4,993,482 describes the use of highly conductive springs laid on their sides. Every loop of the springs represents two wires thermally linking the component to the cover plate. Thermal performance is dependent on good thermal contact with the springs and the ability to fill the void between the component and the cover plate with thermal links. U.S. Pat. No. 4,156,458 also describes a similar system using a tubular roll of foil instead of a spring.
IBM Technical Disclosure Bulletin article entitled xe2x80x9cLSI Cooling and Packaging Designxe2x80x9d dated February, 1994, pages 99-100, and U.S. Pat. No. 5,528,456 describe other designs using corrugated sheets of highly conductive materials to interface between the component and the cover plate. The corrugations deform to accommodate height and tilt variations.
U.S. Pat. Nos. 5,557,501 and 5,650,914 describe a system where a plurality of foil cantilevers are fabricated on thermally conductive plates using conventional photolithography and etching techniques. The cantilevers are bonded between the plates to produce a plurality of short thermal links similar to the corrugations described previously. Half of the cantilevers are made in opposite lateral directions to substantially neutralize lateral forces on the component. Multi-layered cantilevers are also described. Their ability to fill the void between the component and the cover plate, however, remains lower than U.S. Pat. Nos. 4,485,429 and 4,156,458 described previously.
Similar interface devices for use between curved or cylindrical surfaces, such as traveling wave tubes and heat pipes, are described in U.S. Pat. Nos. 3,746,087 and 3,823,772. Cone-shaped structures, anchored circumferentially to the inside surface of a cylindrical cavity, are metallurgically bonded to a coaxially aligned cylindrical component producing a permanent installation. A design is also described that uses thin fins bonded tangentially to a cylindrical component. U.S. Pat. No. 4,358,707 describes a plurality of angled cantilevers machined into the outer surface of a cylindrical heat generating component.
Despite the wide variety of existing designs, a need continues for improved interface devices that provide high conduction cooling capabilities between two generally flat surfaces while accommodating a range of gap distances and angular misalignment (tilt) between the surfaces. A need also exists for similar devices to interface between curved or variously-shaped surfaces to provide similar benefits.
The present invention sets out to address these needs.
According to one aspect of the invention there is provided an interface device, comprising:
at least one foil assembly, with each foil assembly comprised of a plurality of flexible foils, the foils extending between a first surface and a second surface and in a length direction along the surfaces, with each foil comprised of a proximal edge near the first surface, a flexing section, and a distal edge near the second surface, the foils within the foil assembly are stacked in a densely-packed, nested fashion with the proximal edges of adjacent foils distributed with a proximal edge spacing factor and the distal edges of adjacent foils distributed with a distal edge spacing factor so that interstitial separation distances are provided between the flexing sections of adjacent foils to accommodate flexing and compression of the distance between the first and second surfaces to a desired minimum for the foil assembly.
This invention also considers the interface device as defined above wherein the interstitial separation distances are generally depleted and the flexing sections of adjacent foils are generally against each other when the distance between the first and second surfaces is at the desired minimum for the foil assembly. This invention also considers the interface device as defined above wherein the relative spacing between adjacent proximal edges and the relative spacing between adjacent distal edges remains generally fixed during device operation. This invention also considers the interface device as defined above wherein the proximal edges of the foils are fixed by bonding the proximal edges of adjacent foils together, and/or by bonding the proximal edges to a common bonding surface such as a first member. The first member may be, for example, a heat generating component, a heat sink, a cover plate, or a collector plate. The bonded plurality of adjacent proximal edges, and/or the first member (with its bonds to the proximal edges of the foils) may also be flexible and deformable in a direction perpendicular to the foil length direction. This provides a capacity for the first surface of the foil assembly to bend and conform to a range of curved surfaces. This invention also considers the interface device as defined above wherein at least one of the first and second surfaces is(are) curved in a direction perpendicular to the foil length direction.
This invention also considers the interface device as defined above with the foil flexing sections further comprised of at least one bend. This invention also considers the interface device as defined above where the surfaces of the foils, excluding the proximal and distal edges, are coated.
This invention also considers the interface device as defined above further comprising a means for increasing springback to exert added force on the foil assembly to extend the distance between the first and second surfaces. The means for increasing springback may comprise helical springs, foil-shaped springs or foil-shaped spring assemblies. Pluralities of both elastically deformable foils and elastoplastically deformable foils may be combined in one interface device to provide both thermal performance and springback.
According to a further aspect of the invention there is provided a method of making an interface device, comprising the steps of:
pre-forming a plurality of flexible foils in a shape generally similar to their shape in a foil assembly when the distance between a first surface and a second surface is a desired minimum, and each foil being comprised of a proximal edge near the first surface, a flexing section and a distal edge near the second surface;
stacking the plurality of foils in a densely-packed, nested fashion;
fixing the relative spacing between adjacent foil distal edges and fixing the relative spacing between adjacent foil proximal edges;
extending the distance between the first surface and the second surface.
This intention also considers the method of making an interface device as defined above wherein the foils are stacked in a densely-packed, nested fashion with the flexing sections of adjacent foils directly against each other.
According to a further aspect of the invention there is provided a further method for manufacturing an interface device, comprising the steps of:
pre-forming a plurality of flexible foils in a shape generally similar to their shape in a foil assembly when the distance between a first surface and a second surface is greater than a desired minimum, and each foil comprised of a proximal edge near the first surface, a flexing section and a distal edge near the second surface;
stacking the plurality of foils in a densely-packed, nested fashion between at least one proximal die and at least one distal die, with the proximal die(s) having a surface generally similar in shape to the desired shape for the first surface and the distal die(s) having a surface generally similar in shape to the desired shape for the second surface and the foils extending generally between the proximal and distal dies;
compressing the plurality of foils between the proximal and distal dies and allowing the stack of foils to spread out and the foils to deform until the distance between the first surface and the second surface is a desired minimum;
fixing the relative spacing between adjacent foil distal edges and fixing the relative spacing between adjacent foil proximal edges produced when the distance between the first surface and the second surface is at the minimum; and
extending the foil assembly by extending the distance between the first surface and the second surface.
This invention also considers the method of making an interface device as defined above wherein the flexing sections of adjacent foils directly against each other when fixing the foil edges.
According to a further aspect of the present invention there is provided a tubular interface device, comprising:
at least one foil assembly, with each foil assembly comprised of a plurality of flexible foils, and the foils extending generally parallel to the central axis of the device and extending between a tubularly-shaped first surface and a tubularly-shaped second surface, and each foil comprised of a proximal edge near the tubularly-shaped first surface, a flexing, section with at least one bend, and a distal edge near the tubularly-shaped second surface, and the foils within at least one of the foil assemblies are stacked in a densely-packed, nested fashion, with the distal edges of adjacent foils distributed with a distal edge spacing factor and generally fixed relative to each other, and the proximal edges of adjacent foils distributed with a proximal edge spacing factor and generally fixed relative to each other, and the spacing factors providing interstitial separation distances between the flexing sections of adjacent foils to accommodate deformation and compression of the foils and a reduction in the distance between the tubularly-shaped first and second surfaces to a desired minimum for the foil assembly.
This invention also considers the interface device as defined above wherein the tubularly-shaped first surface is not continuous, the first surface being comprised of at least one split extending generally parallel to the central axis of the device for its entire length, and proximal edges of foils on opposite sides of the split(s) are not fixed relative to each other, so as to allow expansion in the general diameter of the tubularly-shaped first surface. This invention also considers the interface device as defined above further comprising a tubularly-shaped proximal collector plate, the proximal collector plate being comprised of at least one split extending parallel to its central axis and for its entire length, and proximal edges of foils on opposite sides of the split(s) are not fixed relative to each other. This invention also considers the interface device as defined above wherein the interstitial separation distances are generally depleted and the flexing sections of adjacent foils within a foil assembly are generally against each other when the distance between the tubularly-shaped first surface and the tubularly-shaped second surface is a desired minimum for the foil assembly. This invention also considers the interface device as defined above further comprising a means for increasing springback such as at least one garter spring.
According to a further aspect of the present invention there is provided a tubular interface device, comprising:
an outer shell;
at least one foil bundle, with each foil bundle comprised of a plurality of flexible foils, and each foil comprised of a proximal edge near an inner tubularly shaped surface, a flexing section, and a distal edge near the outer shell, the foils within at least one of the foil bundles are stacked in a densely-packed, nested fashion, with the stack extending generally parallel to the axis of the device, with each foil bundle compressible from a smaller radial distance from the central axis of the device to a larger radial distance, and the proximal edges of adjacent foils within a foil bundle generally fixed at a proximal edge spacing factor to each other and the distal edges of adjacent foils within a foil bundle generally fixed at a distal edge spacing factor to each other and the distal edges fixed to the outer shell, so that interstitial separation distances are provided between the flexing sections of adjacent foils to accommodate flexing and compression of the distance between the inner tubularly-shaped surface and the outer shell to a desired minimum for the foil bundle.
This invention also considers the interface device as defined above wherein the flexing sections of adjacent foils are generally against each other and the interstitial separation distances are depleted when the distance between the inner tubularly-shaped surface and the outer shell is at the desired minimum for the foil bundle. This invention also considers the interface device as defined above wherein the proximal edges of the foils within a foil bundle are bonded to a first member. This invention also considers the interface device as defined above further comprising a means for increasing springback.